Martin et al., U.S. Pat. No. 4,228,050, discloses a complex molding composition for the compression molding of high density information records such as CEDs. This composition, in essence, comprises a thermoplastic resin, preferably a vinyl chloride-based polymer or copolymer, and sufficient finely divided conductive carbon black to provide capacitive playback of discs prepared therefrom. Typically, such compositions have a bulk resistivity of below about 500 ohm-cm at 900 mHz. The composition disclosed by Martin et al. additionally contains both liquid and solid additives such as stabilizes, lubricants, plasticizers, processing aids and the like. In addition to the function of these ingredients in the formulation, e.g. as a lubricant, the selection of each required consideration of their stability during the processing and molding of the formulation and the possibility of reactions among any two or more ingredients and/or their degradation or reaction products.
It will be appreciated that, because of the numerous possibilities for reactions in a large formulation such as disclosed by Martin et al, particularly in the heat and pressure of the molding process, it would be advantageous to significantly reduce the number of ingredients there. Datta, in copending application Ser. No. 452,915, filed Dec. 12, 1982, and Labib et al., in copending application Ser. No. 549,560, filed Nov. 7, 1983, now abandoned, disclose improved formulations containing few ingredients. The simplified formulations disclosed in these applications additionally possess other advantages such as avoiding the need for the conventional step of washing the surface of the disc after pressing.
In accordance with this invention, a specific plasticizer has been found which further improves CED conductive molding compositions.